This invention relates generally to circuit breakers and, more particularly, to arc detection in residential circuit breakers.
Circuit breakers typically are used in residences in order to prevent abnormal operation of a residential circuit to protect residential wiring, e.g., in the wall wiring, power outlet connectors, extension cords, appliance cords and appliances. Although detection of arcs is desirable to reduce the possibility of a fire being started by an arc and to protect residential wiring, known residential circuit breakers typically do not include an arc detection unit.
Circuit breakers systems typically comprise a main circuit breaker line, and several branch circuit breaker lines. More specifically, arcs generally can be identified by the high frequency content of current flowing in a branch line. High frequency current, e.g., current having a frequency exceeding the range of 1 KHz to 10 MHz, can be introduced into the branch line, however, through many benign apparatuses such as universal motors in hair dryers, drills, and vacuum cleaners. Such motors can produce significant high frequency energy due to the arcing of the brush motor commutation. Silicon controlled rectifier lamp dimmers and advanced electronic devices can also generate high frequency energy. Discriminating between actual arcing faults and benign sources of high frequency energy therefore is much more difficult than just sensing a high frequency. A residential arc detection unit, however, must have a low false alarm rate. Known arc detection units having the necessary low false alarm rate are expensive.
To reduce the costs of arc detection units, some known circuit breakers include central processing units that execute algorithms to eliminate possible noise sources, such as electric household appliances and tools (e.g., motors, welders, switches). Such known algorithms utilize Fourier analysis and other frequency domain based approaches. The noise sources are eliminated from the primary signal by classifying the noise resulting from such sources, and then using such classified signals to identify noise signals and sources in the primary signal. The noise signals are then subtracted from the primary signal so that the noise portion of the signal is eliminated.
The functional requirements for digital signal processing based on the elimination of noise sources requires correct classification of noise signals followed by the storage of data, i.e., storage of the portion of the primary signal associated with the noise signal. The processing power necessary to provide this function is high and increases proportionately with the number of noise sources present as well as the frequency range used because of Fourier Transform calculation requirements.
In one known analog breaker configuration, tripping occurs when 4 or more arc pulses are detected in a sliding 0.5 second window. Under certain conditions, such as lamp burnout, two consecutive high current arc pulses are generated that are known to cause false unit tripping. It would be desirable to provide methods and apparatus for reducing false tripping of an analog breaker configuration arc protection at a low cost as compared to the costs associated with using sophisticated arc detection units.